1. Field of the Invention
This invention relates to a magnetic recording medium formed with a groove as a tracking controlling guide groove, and to a magnetic recording/reproducing apparatus for recording/reproducing the magnetic recording medium. The present invention also relates to a method for manufacturing a metallic mold for molding a disc as a master for a substrate of a magnetic recording medium.
2. Description of Related Art
In the field of a magnetic recording medium, development of such magnetic recording medium having pits corresponding to servo signals is proceeding for realization of a higher recording density. The pits corresponding to servo signals means crests and recesses pre-formed on the substrate of the magnetic recording medium during molding thereof in association with the servo signals.
In the magnetic recording medium having these pits formed therein, the crests and recesses are magnetized to opposite polarities before using the recording medium for recording/reproduction for writing the servo signals. Since these pits can be formed to extremely high accuracy, it becomes possible to write the servo signals highly accurately by pre-forming pits corresponding to the servo signals on the substrate. That is, servo signals can be written at extremely correct positions on the recording tracks thus enabling high-density recording more easily than with a conventional magnetic recording medium. In the following description, a zone in which to write these servo signals is termed a servo zone.
In the magnetic recording medium having these pits formed therein, there are usually formed a plurality of grooves for extending along recording tracks. The groove herein means a groove-shaped recessed portion formed along the recording track and is formed in a zone other than the servo zone. That is, the groove is formed in an area of the recording track in which data is recorded or reproduced by the user. The projecting portion defined between the grooves is termed a land on which the major portion of data recorded or reproduced by the user is recorded. In the following description, an area in which the above groove is formed and which is used for data recording/reproduction by the user is termed a data zone.
For data recording/reproduction on or from a magnetic recording medium using a magnetic head, a magnetic head is arranged on a magnetic recording medium which is rotated at a high velocity. The magnetic head at this time is floated under the effect of an airstream generated by such rotation. For stabilized recording/reproduction on or from the magnetic recording medium, the amount of this float is preferably kept constant.
However, with the magnetic recording medium having the pits or the groove formed therein as described above, it is difficult to keep the amount of float of the magnetic head constant because of irregular formations on the medium surface. In particular, in a magnetic recording medium having a servo zone and a data zone, since the proportion of the crests and recesses in the servo zone formed with the pits differs from that of the lands and the recessed portions in the data zone formed with the grooves, the amount of float of the magnetic head over the servo zone differs from that over the data zone.
It is noted that the height of a pit is equal to or higher than the height of the texture formed on a recording medium in a conventional hard disc device. Also, the length of the pit is of the order of several micrometers which is equivalent to that of the texture. Thus, the magnetic recording medium in which the proportion of the crests and recesses in the servo zone formed with the pits differs from that of the lands and the recessed portions in the data zone formed with the groove has a non-uniform texture state.
The result is that the amount of float of the magnetic head over the servo zone differs from that over the data zone, thus producing variations in the amount of float of the magnetic head during recording/reproduction to render it difficult to perform stabilized recording/reproduction. This problem is inherent in a magnetic recording medium having pre-formed pits, while it cannot occur in a magnetic recording medium having an overall planar surface. Specifically, with a magnetic recording medium having preformed pits or grooves, it is imperative to suppress fluctuations in the amount of float of the magnetic head.
In a magnetic head in which the data zone is formed with the groove and thus presents an irregular surface, the amount of float of the magnetic head is varied under the effect of the crests and recesses, thus considerably varying off-track characteristics. From this it may be easily surmised that, in the grooved portion representing recessed portions, the separation from the magnetic head is increased to lower the output. Therefore, in a magnetic head in which the data zone presents an irregular surface due to the grooves, it is necessary to prevent the off-track margin from being lowered under the effect of the groove.